DES MOINES, Iowa - With time running short, Republican presidential candidates Rick Santorum and Rick Perry battled Thursday to win over a pivotal crop of undecided conservative voters. Of all the candidates, only Mitt Romney seemed to largely escape attack as he worked to win a state that long seemed out of reach until this week.

"Don't settle for what's not good enough to save the country," the newly ascendant Santorum implored Iowans at city hall in Coralville, urging voters to put conservative principles above everything else and suggesting that his rivals, and specifically Ron Paul, lacked them.

Now a target

For the first time, though, the former Pennsylvania senator became a target.

"When he talks about fiscal conservatism, every now and then it leaves me scratching my head because he was a prolific earmarker," said Perry, the Texas governor, referring to special spending projects members of Congress seek. "He loaded up his bill with Pennsylvania pork.'"

Santorum defended the practice as part of lawmakers' constitutional role as appropriators, telling CNBC that he owed it to Pennsylvanians to bring money to the state. He said earmarking became abused and that he would support a ban on them if he were president.

Lack of unity

The maneuvering underscored the fluid - if not convoluted - state of the GOP presidential race as Tuesday's caucuses loom while cultural conservatives and evangelical Republicans, who make up the base of the electorate here, continue to be divided. That lack of unity paves the way for someone who is seen as less consistently conservative.

Five days out, public and private polling show Romney and Paul in strong contention to win the caucuses, with coalitions of support cobbled together from across the Republican political spectrum and their get-out-the-vote operations - beefed up from their failed 2008 bids - at the ready. They're the only two with the money and the organizations necessary to ensure big turnouts on Tuesday.

Three others - Santorum, Perry and Gingrich - will have to rely largely on momentum to carry supporters to precinct caucuses. Each was working to convince fickle conservatives that he alone would adhere strictly to GOP orthodoxy.

Bachmann, meanwhile, worked to convince backers that her cash-strapped campaign was not in disarray after a top supporter in Iowa abandoned her to back Paul.